Florida B.E.S.T. MA.1.NSO.2.5

Math1st GradeDevelop an understanding of addition and subtraction operations with one- and two-digit numbers.

The Standard

Explore subtraction of a one-digit number from a two-digit number.

Florida B.E.S.T. Standards for Mathematics

Teacher's field guide

What Students Need to Do: Students subtract a one-digit number from a two-digit number using objects, drawings, or a number line. They try strategies such as counting back, breaking apart, or making a ten.
What Mastery Looks Like: Students solve problems such as 16 − 7 and 28 − 5 using objects, drawings, or number lines. They explain how counting back or making a ten leads to the answer.
Common Misconceptions: Students may count the starting number as the first step when counting back. They may subtract the smaller digit from the larger digit, or forget that crossing a ten changes the tens digit.
How to Assess It: Ask: “Show 24 − 7 with a drawing or number line. Write the answer and explain how you crossed the ten.”

Lesson moves

Build 32 with base-ten blocks, trade one ten for ten ones, remove 6 ones, and record the matching equation.
Ask, “How are 24 − 3 and 24 − 7 alike and different?” Students draw both and explain their thinking.
Play Subtraction Match by drawing a two-digit number card and a one-digit card, solving, then finding the matching answer card.
Give students 26 crayons, remove 8 for another table, and have them model and solve how many remain.

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